The present invention relates to apparatus for detecting the presence of flame and/or smoke, or radiation absorbing vapors, utilizing a single radiation detection tube.
U.S. Pat. No. 3,952,196, issued Apr. 20, 1976 and owned by the assignee of the present invention, discloses a device for determining whether the optical surfaces through which radiation must travel from a hazardous area of radiation to the radiation detector are free from radiation-absorbing material or radiation-blocking material. The device disclosed in this patent includes an enclosure for commonly housing both an auxiliary light source and a radiation detector tube, while isolating the same from each other, preventing radiation transmission within the housing from the light source to the detector. The patent also discloses a radiation path from the light source outwardly from the housing to a reflective surface or surfaces external of the housing, which surfaces reflect at least some of the radiation back to the detector through the same optical surfaces that other external radiation passes. The patent contemplates external reflective surfaces which either form a part of the outside housing structure, or are remotely located therefrom.
U.S. patent application No. 289,813, filed Aug. 3, 1981, now U.S. Pat. No. 4,405,234 and owned by the assignee of the present invention, discloses a radiation detector tube enclosed in a housing having a light transparent window at one end thereof, with an auxiliary light source enclosed within the housing in optical isolation with respect to the radiation detection tube. The transparent window is constructed with a beveled edge surface and the auxiliary light source is positioned so as to radiate light through the beveled edge, a portion of which is reflected backwards from the interface surface of the front of the transparent window and back through the diametrically-opposite beveled edge of the transparent window. An internal mirrored surface is positioned to collect and reflect the light so received, and to direct the light radiation to the detection tube. The invention provides a self-checking feature for the radiation detection tube and the optical path to the radiation detection tube to the point of interface with the external environment, through a totally-enclosed construction.